This invention relates to electrochromic elements as utilized within rearview mirror assemblies for motor vehicles, as well as within window assemblies, and more particularly, to improved electrochromic elements for use within such assemblies. More particularly, the present invention relates to electrochromic elements that include conductive layers deposited at atmospheric pressure without compromising associated bulk conductivity values.
Heretofore, various rearview mirrors for motor vehicles have been proposed which change from the full reflectance mode (day) to the partial reflectance mode(s) (night) for glare-protection purposes from light emanating from the headlights of vehicles approaching from the rear. Similarly, variable transmittance light filters have been proposed for use in architectural windows, skylights, within windows, sunroofs, and rearview mirrors for automobiles, as well as for windows or other vehicles such as aircraft windows. Among such devices are those wherein the transmittance is varied by thermochromic, photochromic, or electro-optic means (e.g., liquid crystal, dipolar suspension, electrophoretic, electrochromic, etc.) and where the variable transmittance characteristic affects electromagnetic radiation that is at least partly in the visible spectrum (wavelengths from about 3800 Å to about 7800 Å). Devices of reversibly variable transmittance to electromagnetic radiation have been proposed as the variable transmittance element in variable transmittance light-filters, variable reflectance mirrors, and display devices, which employ such light-filters or mirrors in conveying information.
Devices of reversibly variable transmittance to electromagnetic radiation, wherein the transmittance is altered by electrochromic means, are described, for example, by Chang, “Electrochromic and Electrochemichromic Materials and Phenomena,” in Non-emissive Electrooptic Displays, A. Kmetz and K. von Willisen, eds. Plenum Press, New York, N.Y. 1976, pp. 155-196 (1976) and in various parts of Electrochromism, P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, VCH Publishers, Inc., New York, N.Y. (1995). Numerous electrochromic devices are known in the art. See, e.g. Manos, U.S. Pat. No. 3,451,741; Bredfeldt et al., U.S. Pat. No. 4,090,358; Clecak et al., U.S. Pat. No. 4,139,276; Kissa et al., U.S. Pat. No. 3,453,038; Rogers, U.S. Pat. Nos. 3,652,149, 3,774,988 and 3,873,185; and Jones et al., U.S. Pat. Nos. 3,282,157, 3,282,158, 3,282,160 and 3,283,656. In addition to these devices, there are commercially available electrochromic devices and associated circuitry, such as those disclosed in U.S. Pat. No. 4,902,108, entitled “SINGLE-COMPARTMENT, SELF-ERASING, SOLUTION-PHASE ELECTROCHROMIC DEVICES SOLUTIONS FOR USE THEREIN, AND USES THEREOF,” issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No. 1,300,945, entitled “AUTOMATIC REARVIEW MIRROR SYSTEM FOR AUTOMOTIVE VEHICLES,” issued May 19, 1992, to J. H. Bechtel et al.; U.S. Pat. No. 5,128,799, entitled “VARIABLE REFLECTANCE MOTOR VEHICLE MIRROR,” issued Jul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled “ELECTRO-OPTIC DEVICE,” issued Apr. 13, 1993, to H. J. Byker et al.; U.S. Pat. No. 5,204,778, entitled “CONTROL SYSTEM FOR AUTOMATIC REARVIEW MIRRORS,” issued Apr. 20, 1993, to J. H. Bechtel; U.S. Pat. No. 5,278,693, entitled “TINTED SOLUTION-PHASE ELECTROCHROMIC MIRRORS,” issued Jan. 11, 1994, to D. A. Theiste et al.; U.S. Pat. No. 5,280,380, entitled “UV-STABILIZED COMPOSITIONS AND METHODS,” issued Jan. 18, 1994, to H. J. Byker; U.S. Pat. No. 5,282,077, entitled “VARIABLE REFLECTANCE MIRROR,” issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376, entitled “BIPYRIDINIUM SALT SOLUTIONS,” issued Mar. 15, 1994, to H. J. Byker; U.S. Pat. No. 5,336,448, entitled “ELECTROCHROMIC DEVICES WITH BIPYRIDINIUM SALT SOLUTIONS,” issued Aug. 9, 1994, to H. J. Byker; U.S. Pat. No. 5,434,407, entitled “AUTOMATIC REARVIEW MIRROR INCORPORATING LIGHT PIPE,” issued Jan. 18, 1995, to F. T. Bauer et al.; U.S. Pat. No. 5,448,397, entitled “OUTSIDE AUTOMATIC REARVIEW MIRROR FOR AUTOMOTIVE VEHICLES,” issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No. 5,451,822, entitled “ELECTRONIC CONTROL SYSTEM,” issued Sep. 19, 1995, to J. H. Bechtel et al. Each of these patents is commonly assigned with the present invention and the disclosures of each, including the references contained therein, are hereby incorporated herein in their entirety by reference. Such electrochromic devices may be utilized in a fully integrated inside/outside rearview mirror system or as separate inside or outside rearview mirror systems, and/or variable transmittance windows.
FIG. 1 shows the cross-section of a typical electrochromic mirror device 10, having a front planar substrate 12 and a rear planar substrate 16, and of which the general layout is known. A transparent conductive coating 14 is provided on the rear surface of the front substrate 12, and another transparent conductive coating 18 is provided on the front surface of rear substrate 16. A reflector 20, typically comprising a silver metal layer 20a covered by a protective copper metal layer 20b, and one or more layers of protective paint 20c, is disposed on the rear surface of the rear substrate 16. For clarity of description of such a structure, the front surface 12a of the front substrate 12 is sometimes referred to as the first surface, and the inside (or rear) surface 12b of the front substrate 12 is sometimes referred to as the second surface, the inside surface 16a of the rear substrate 16 is sometimes referred to as the third surface, and the back surface 16b of the rear substrate 16 is sometimes referred to as the fourth surface. In the illustrated example, the front substrate further includes an edge surface 12c, while the rear substrate includes an edge surface 16c. The front and rear substrates 12,16 are held in a parallel and spaced-apart relationship by seal 22, thereby creating a chamber 26. The electrochromic medium 24 is contained in space or chamber 26. An electrochromic medium 24 is in direct contact with transparent electrode layers 14 and 18, through which passes electromagnetic radiation whose intensity is reversibly modulated in the device by a variable voltage or potential applied to electrode layers 14 and 18 through clip contacts and an electronic circuit (not shown).
The electrochromic medium 24 placed in chamber 26 may include surface-confined, electrode position-type or solution-phase-type electrochromic materials and combinations thereof. In an all solution-phase medium, the electrochemical properties of the solvent, optional inert electrolyte, anodic materials, cathodic materials, and any other components that might be present in the solution are preferably such that no significant electrochemical or other changes occur at a potential difference which oxidizes anodic material and reduces the cathodic material other than the electrochemical oxidation of the anodic material, electrochemical reduction of the cathodic material, and the self-erasing reaction between the oxidized form of the anodic material and the reduced form of the cathodic material.
In most cases, when there is no electrical potential difference between transparent conductors 14 and 18, the electrochromic medium 24 in chamber 26 is essentially colorless or nearly colorless, and incoming light (I0) enters through the front substrate 12, passes through the transparent coating 14, the electrochromic medium 24 in chamber 26, the transparent coating 18, the rear substrate 16, and reflects off the layer 20a and travels back through the device and out the front substrate 12. Typically, the magnitude of the reflected image (IR) with no electrical potential difference is about 45 percent to about 85 percent of the incident light intensity (I0). The exact value depends on many variables outlined below, such as, for example, absorption by the various components, the residual reflection (I′R) from the front face of the front substrate, as well as secondary reflections from the interfaces between the front substrate 12 and the front transparent electrode 14, the front transparent electrode 14 and the electrochromic medium 24, the electrochromic medium 24 and the second transparent electrode 18, and the second transparent electrode 18 and the rear substrate 16. These reflections are well known in the art and are due to the difference in refractive indices between one material and another as the light crosses the interface between the two. If the front substrate and the back element are not parallel, then the residual reflectance (I′R) or other secondary reflections will not superimpose with the reflected image (IR) from mirror surface 20a, and a double image will appear (where an observer would see what appears to be double (or triple) the number of objects actually present in the reflected image).
There are minimum requirements for the magnitude of the reflected image depending on whether the electrochromic mirrors are placed on the inside or the outside of the vehicle. For example, according to current requirements from most automobile manufacturers, inside mirrors preferably have a high end reflectivity of at least 70 percent, and outside mirrors must have a high end reflectivity of at least 35 percent.
The electrode layers 14 and 18 are connected to electronic circuitry which is effective to electrically energize the electrochromic medium, such that when a potential is applied across the conductors 14 and 18, the electrochromic medium in chamber 26 darkens, such that incident light (I0) is attenuated as the light passes toward the reflector 20a and as it passes back through after being reflected. By adjusting the potential difference between the transparent electrodes, such a device can function as a “gray-scale” device, with continuously variable transmittance over a wide range. For solution-phase electrochromic systems, when the potential between the electrodes is removed or returned to zero, the device spontaneously returns to the same, zero-potential, equilibrium color and transmittance as the device had before the potential was applied. Other electrochromic materials are available for making electrochromic devices. For example, the electrochromic medium may include electrochromic materials that are solid metal oxides, redox active polymers, and hybrid combinations of solution-phase and solid metal oxides or redox active polymers; however, the above-described solution-phase design is typical of most of the electrochromic devices presently in use.
Even before a fourth surface reflector electrochromic mirror such as that show in FIG. 1, was commercially available, various groups researching electrochromic devices had discussed moving the reflector from the fourth surface to the third surface. Such a design has advantages in that it should, theoretically, be easier to manufacture because there are fewer layers to build into a device, i.e., the third surface transparent electrode is not necessary when there is a third surface reflector/electrode. Although this concept was described as early as 1966, no group had commercial success because of the exacting criteria demanded from a workable auto-dimming mirror incorporating a third surface reflector. U.S. Pat. No. 3,280,701, entitled “OPTICALLY VARIABLE ONE-WAY MIRROR,” issued Oct. 25, 1966, to J. F. Donnelly et al. has one of the earliest discussions of a third surface reflector for a system using a pH-induced color change to attenuate light.
U.S. Pat. No. 5,066,112, entitled “PERIMETER COATED, ELECTRO-OPTIC MIRROR,” issued Nov. 19, 1991, to N. R. Lynam et al., teaches an electro-optic mirror with a conductive coating applied to the perimeter of the front and rear glass elements for concealing the seal. Although a third surface reflector is discussed therein, the materials listed as being useful as a third surface reflector suffer from the deficiencies of not having sufficient reflectivity for use as an inside mirror, and/or not being stable when in contact with a solution-phase electrochromic medium containing at least one solution-phase electrochromic material.
Others have broached the topic of a reflector/electrode disposed in the middle of an all solid state-type device. For example, U.S. Pat. Nos. 4,762,401, 4,973,141, and 5,069,535 to Baucke et al. teach an electrochromic mirror having the following structure: a glass element, a transparent indium-tin-oxide electrode, a tungsten oxide electrochromic layer, a solid ion conducting layer, a single layer hydrogen ion-permeable reflector, a solid ion conducting layer, a hydrogen ion storage layer, a catalytic layer, a rear metallic layer, and a back element (representing the conventional third and fourth surface). The reflector is not deposited on the third surface and is not directly in contact with electrochromic materials, certainly not at least one solution-phase electrochromic material and associated medium. Consequently, it is desirable to provide an improved high reflectivity electrochromic rearview mirror having a third surface reflector/electrode in contact with a solution-phase electrochromic medium containing at least one electrochromic material. Electrochromic windows that have been proposed, typically include an electrochromic cell similar to that shown in FIG. 1, but without layer 20a, 20b and 20c. 
Whether deposited on the first, second, third, fourth or edge surfaces of the substrates, metal containing films or layers that are conductive, reflective, or both are significantly useful in the construction of electrochromic electro-optic devices as well as the integrated electrochromic devices packaged therewith. Generally, the versatility and utility of a metal film or multiple layers of metal films increases: as the conductivity increases; as the adhesive properties increase; as the intricacy of the pattern of the layer increases; as the reflectivity increases while maintaining a color neutral reflection; as the chemical and electrochemical stability increases; and, as the ease of application increases.
Various attempts have been made to provide an electrochromic element with conductive layers on the surfaces of the substrates associated with an electrochromic element as discussed above. One such method includes utilizing metal particle load resins such as epoxy resins loaded with silver flake. However, the conductivity of such systems is limited by the sheer number of particle to particle connections that must be made in order to conduct current. Each particle to particle connection adds electrical resistance, thereby limiting the usefulness of metal particle loaded resins. Currently, it is not possible to obtain mirror-quality specular light reflection from such films since the random orientation of the relatively large metal particles promotes diffuse reflection. In order to avoid these limitations, it is desirable to deposit metal films that more closely approach bulk metal properties. Metal films that more closely approach bulk metal properties for conduction and reflection adhere well to applicable substrates, are chemically and electro-chemically durable, and can be deposited using vacuum processes such as sputtering or evaporation. However, the equipment for vacuum-based processes is expensive to purchase, operate, and maintain. It is further difficult to deposit pattern films using vacuum-based processes. One method of patterning vacuum-applied metal films requires that the metal be applied through a mask during deposition. Such masks can be expensive to machine and difficult to maintain. Another method of patterning a vacuum-applied metal film requires that the metal be removed after deposition by additional processing steps such as laser ablation or chemical etching. Aside from increasing the complexity of the overall manufacturing process, the aforementioned sputtering or evaporation processes are also not efficient in the use of metal or metal precursors. Specifically, a significant amount of metal is deposited on the masking and surrounding structure rather than on the desired device during the vacuum processing, the reclamation of the which is costly and time consuming.
It is therefore desirable to produce metal films within electrochromic or other electro-optic devices under near atmospheric conditions, and specifically atmospheric pressure, and that provide adequate conductive, adhesive and reflective properties, while maintaining a color neutral reflection, adequate chemical and electrochemical stability, and simultaneously allowing for an increase in application control.